The present disclosure relates generally to electric power generation and more particularly to electric power generation systems including magnetically geared machines.
Electrical machines such as motors and generators typically deliver more power at high speeds than at low speeds. In order to adapt a high-speed, rotating electrical machine to a high-torque, lower speed mechanical component (such as a prime mover in the case of a generator or a load in the case of a motor), mechanical gear boxes are typically selected because the cost of having a high-speed electrical machine coupled with mechanical gearing for speed/torque conversion is lower than the cost of a low-speed electrical machine. Mechanical gearing has some inherent disadvantages with respect to acoustic noise, vibration, reliability, and maintenance, for example.
Magnetic gears do not require physical contact between an input shaft and an output shaft but have traditionally received relatively little attention in the industry due to design complexities and limitations on torque density. For example, a magnetic gear assembly arranged in a spur configuration results in only a small fraction of the permanent magnets located on the gears actually contributing to torque conversion at any given time.
In commonly assigned U.S. 20070186692, a machine includes a moveable rotor having a first magnetic field associated therewith, a stator configured with a plurality of stationary stator windings therein, and a magnetic flux modulator interposed between the moveable rotor and the stator windings. The magnetic flux modulator is configured to transmit torque between the first magnetic field associated with the moveable rotor and a second magnetic field excited by the plurality of stationary stator windings. Such magnetically geared generators are capable of generating electric power from a prime mover under conditions of low speed and high torque and doing so without the need of a gearbox or speed adapter. However, due to flux leakage and magnetic coupling challenges, magnetically geared generators have higher reactance and lower induced emf than most conventional generators as well as an intrinsically low power factor (for example, below 0.7 or even more typically in the range of 0.2 to 0.5).
It would be desirable to have a technical and cost effective method of obtaining the benefits of magnetically geared generators while overcoming the aforementioned power factor drawback.